A South Korean human rights commission said on Monday it will investigate whether a dozen North Korean restaurant workers who defected to the South two years ago came of their own free will or were tricked or coerced by an intelligence agent.

The 12 waitresses and their manager left a North Korean state-run restaurant in China to come via Malaysia to South Korea in April 2016.

Seoul promptly announced their defection, but North Korea says they were abducted by South Korean agents and demands their repatriation.

The restaurant manager has previously told South Korean news agency Yonhap and other media that an agent from South Korea’s spy agency National Intelligence Service (NIS) used persuasion and threats to get him to enter the South with the workers.

Some of the workers say they were unaware they were entering South Korea until they arrived at the South Korean embassy in Malaysia, the independent National Human Rights Commission of Korea said.

The rights group has mounted a first state probe into the case in the wake of calls by a liberal interest group of lawyers and from Tomas Ojea Quintana, the United Nations’ Human Rights Special Rappoteur on North Korea.

The issue has complicated efforts to improve relations between the two Koreas.

North Korean state newspaper Rodong Shinmun and propaganda website Uriminzokkiri have said that unless the restaurant workers are returned there could be an “obstacle” to the reunion, planned to take place next month, of families divided by the 1950-53 Korean war.

South Korea’s Unification Ministry has previously said it was informed from intelligence authorities that the workers came voluntarily, but Unification Minister Cho Myoung-gyon told lawmakers last week that the ministry had not yet met the workers or verified the intelligence officials’ accounts.

The ministry said on Monday its it has been consistently cooperating with the commission’s requests.